Aluminum plates supported by wood or plastic spacers contain channels which accept tubing. These plates spread the heat uniformaly beneath the finished floor. Hardwood floors can be nailed directly to the subfloor plates or carpet and pad placed over the plates. It is also possible to nail a second subfloor over the plates for a smoother finish for vinyl areas. A cement board is used when tile or stone is to be installed. Particle board is not recommended as a subfloor.